Revista Chilena de Historia Natural 76 (2): 177-185, 2003
SIMPOSIUM
Reproductive timing and larval dispersal of intertidal crabs: the predator avoidance
hypothesis
Many intertidal and shallow water crabs have strong reproductive cycles and migratory
larvae. Females release larvae near the time of high water of the larger amplitude nocturnal tides during the semilunar or lunar cycles.
Newly hatched larvae move quickly at night toward and into the sea where, weeks later, they develop to megalopae that then ride
nocturnal flood tides inshore and up estuaries to settle in adult habitats. It was first thought that crabs might time larval release so that
larvae will become megalopae when they can ride the larger amplitude spring flood tides to adult habitats. This idea was rejected when
it was found that were was no change in the timing of hatching during the breeding season by several estuarine species that would
compensate for the decrease in the larval development period as the water temperature increased. In addition, megalopae moved up-
stream at night but not on the largest spring flood tides. Attention shifted to the possible value to larvae of leaving the estuary quickly to
avoid high temperatures, low salinities or stranding. This idea was not supported when it was found that species on open coasts exhibit
the same reproductive patterns as do estuarine species. Alternatively, by moving quickly to the ocean at night larvae may best escape
visual planktivorous fishes that are especially abundant in shallow areas. This predator avoidance hypothesis has been broadly
supported: species with larvae that are cryptic, spiny and better protected from predation lack both strong reproductive cycles and
larval migration. The mechanisms that promote precise reproductive timing have been little studied. Evidence is presented that female
fiddler crabs may adjust the timing of fertilization to compensate for variation in incubation temperatures that would otherwise induce
timing errors. However, crabs on colder coasts, as in Chile, apparently do not exhibit biweekly or monthly cycles of larval release. The
consequences of this for adults and larvae have yet to be explored.
Key words:
larval release, larval
dispersal, crabs, reproductive timing, plankton, predation
